The electrical conductivity and infrared spectroscopic measurement of aqueous solutions of cetyltrimethylammonium bromide (CTAB), cationic surfactant, with imidazolium based ionic liquid 1- butyl-3 methyl imidazolium bromide [C4mim] [Br] were determined at different weight percentages and temperatures. The temperature dependence of critical micelle concentration (cmc) obtained from conductivity measurements at different temperatures (298.15, 303.15, and 308.15) K has been used to calculate various thermodynamic parameters of micellization like standard enthalpy of micellization (ΔHm0), standard free energy of micellization (ΔGm0), and standard entropy of micellization (ΔSm0), and the obtained parameters are further used to understand the effect of ionic liquid on surfactant. The influence of ionic liquid 1-butyl-3-methylimidazolium Bromide [C4mim][Br] on the micellization process of the cetyltrimethylammonium bromide (CTAB) is discussed.